(a) Describe the formation of (i) Erosional plains, (ii) Dissected plateau (b) Highlight two advantages and two disadvantages of plains.

(a)(i) Formation of erosional plains

Erosional (denudation) plains are formed by the long-continued wearing down of a former highland by agents of denudation. Rivers, ice, wind and weathering slowly strip away the raised land over a very long period until the surface is reduced almost to a low, gently undulating plain (a peneplain). Continuous weathering, erosion and transport of the loosened material lowers the land close to base level, leaving occasional resistant remnants (monadnocks) standing above the plain.

(a)(ii) Formation of a dissected plateau

A dissected plateau is formed when an upland or plateau is cut into (dissected) by rivers. After uplift, active rivers flowing across the plateau erode deep, steep-sided valleys and gorges into it. Continued vertical (down-cutting) erosion by many streams divides the once continuous upland surface into separate blocks, ridges, spurs and flat-topped hills, giving a rugged, broken plateau surface.

(b) Advantages and disadvantages of plains

Advantages

• The flat, gentle land encourages agriculture, since it is easy to cultivate and often has deep, fertile alluvial soils.
• They favour settlement and construction of roads, railways and towns because building is easy and cheap.

Disadvantages

• Low, flat plains near rivers are liable to flooding and may become waterlogged/swampy.
• They may suffer poor drainage and, in dry areas, can be exposed and monotonous, encouraging soil erosion by wind or sheet wash.